How to detect HTMLCollection/NodeList in JavaScript?

Question

I'm not sure my current implementation is available all the time:

function isNodeList(nodes) {     var result = Object.prototype.toString.call(nodes);     // modern browser such as IE9 / firefox / chrome etc.     if (result === '[object HTMLCollection]' || result === '[object NodeList]') {         return true;     }     //ie 6/7/8     if (typeof(nodes) != 'object') {         return false;     }     // detect length and item      if (!('length' in nodes) || !('item' in nodes)) {         return false;     }     // use the trick NodeList(index),all browsers support     try {         if (nodes(0) === null || (nodes(0) && nodes(0).tagName)) return true;     }     catch (e) {         return false;     }     return false; } 

A common situation is {length:1,item:function(){return [];}}
The value of result in chrome / safari / opera is '[object NodeList]'.
In firefox and IE 9 , it is '[object HTMLCollection]'.

Which is the standard value?

Answer 1

The following should return true, if nodes is of type NodeList

NodeList.prototype.isPrototypeOf(nodes) 

@DavidSpector, for HTMLCollection you can similarly use :

HTMLCollection.prototype.isPrototypeOf(collection) 

Answer 2

I would structure the code differently:

function isNodeList(nodes) {     var stringRepr = Object.prototype.toString.call(nodes);      return typeof nodes === 'object' &&         /^\[object (HTMLCollection|NodeList|Object)\]$/.test(stringRepr) &&         (typeof nodes.length === 'number') &&         (nodes.length === 0 || (typeof nodes[0] === "object" && nodes[0].nodeType > 0)); } 

Notes:

• less return paths make easier-to-read code
• stick with one type of logic, if possible (i.e. use less negated checks)
• "item" is not mandatorily in a nodeList
• use hasOwnProperty() instead of in
• use square brackets to index into the list
• I don't think a try/catch is really necessary, but that might be wrong - you decide
• check for nodeType instead of tagName, as text nodes or comments do not have a name
• add more checks to the && chain if you see fit